1. Filed of the Invention
The present invention relates to an X-ray imaging apparatus used for medical diagnosis and particularly relates to a portable imaging apparatus having an area sensor serving as an X-ray receiving medium in which multiple photoelectric conversion elements are two-dimensionally arranged on the same plane.
2. Related Background Art
It is a widely used method, in the field of nondestructive inspection for industrial purpose and in the field of medical diagnosis, to obtain a radiation image of an object to be imaged by irradiating the object to be imaged with radiation and detecting the intensity distribution of the radiation that has been transmitted through the object to be imaged. Specifically, a general method of obtaining a radiation image of an object includes the steps of preparing a combination of a silver film and a so-called fluorescent screen (or an intensifying screen) that emits fluorescent light upon receiving radiation, irradiating an object to be imaged with X-rays, converting the transmitted radiation into visible light by means of the fluorescent screen to form an latent image on the silver film, and then chemically processing the silver film to obtain a visible image. The radiation image obtained by this method is an analogue photograph, which is to be used for diagnosis, inspection or other purposes.
On the other hand, recently there has been developed technology for obtaining a digital image using a two dimensional array sensor as image receiving means in which pixels composed of micro photoelectric conversion elements or switching elements are arranged in a lattice-like pattern. Such an imaging apparatus can display obtained image data immediately, so that it may be called a direct X-ray digital imaging apparatus. Advantages of the X-ray digital imaging apparatus over conventional analogue photographing technologies are elimination of the need for films, enlargement of obtained image information realized by image processing and capability of constructing a database etc.
Digital image data obtained from an X-ray digital imaging apparatus is transferred to a system control unit or a storage server etc. via wired or wireless data transmission.
X-ray imaging apparatuses for forming still images for medical use are categorized, based on the scheme of imaging of a patient as an object to be imaged, into stationary type apparatuses and portable type apparatuses. An example of the stationary type apparatus is provided with a table and an imaging portion containing a film or a photoelectric conversion apparatus and it radiates X-rays to a patient from above to obtain an abdominal image of the patient. The portable type apparatus uses a lightweight box called a cassette in which a film is accommodated. The portable type apparatus is used in the case that the condition of a patient is too bad to be brought from a bed in a ward to a table in an X-ray room in which a stationary type apparatus is installed or in the case that a special imaging method that cannot be put into practice by a stationary apparatus is required. In the former case, an operator brings a cassette and an portable X-ray imaging apparatus to the patient's ward, so that the operator performs imaging in the ward.
In view of portability and operationality, it is desirable that the portable apparatus be made as compact and lightweight as possible. However, in the case that the X-ray digital imaging apparatus is to be constructed as a portable apparatus (which will be referred to as an electronic cassette hereinafter), the apparatus includes, in order to output an X-ray transmission image of a patient as a digital image data, many components such as a two-dimensional array sensor for receiving an X-ray image, a drive circuit for driving the sensor in accordance with a control signal sent from an X-ray generating apparatus, an amplifier for selecting matrices within the sensor by means of the drive circuit to amplify the data of each matrix, an A/D conversion circuit for converting the output of the amplifier into digital data and a circuit for serializing the image data that has been sequentially digitized by the A/D converting circuit and the drive circuit. Therefore, it is difficult to make the electronic cassette compact and lightweight as compared to the film cassette. In addition, in the case that wireless data transmission is adopted, a memory for temporally storing data and a battery for supplying power to the electronic cassette are further required. This leads to an additional increase in the size and weight of the electronic cassette. In the case that the number of times of imaging with the electronic cassette is small, the size of the memory and the battery can be made small, so that an increase in the weight may be small. However, in order to eliminate the risk of overflow of memory during imaging and the risk of running out of battery, and since the transfer rate of wireless connection is lower than that of wired connection, the wired connection should also be taken into consideration. On the other hand, in the case that the number of times of imaging is large, it is desirable that the connection scheme be specialized to the wired (or cable) connection, the circuitry for wired data transferring be contained in the electronic cassette, which should be made as compact and lightweight as possible, and a cable for the wired connection be connected to the electronic cassette only at the time of imaging and data transmission.
FIG. 6 shows an example of a state of use of an electronic cassette that can be connected with a cable. The patient P shown in FIG. 6 is a patient lying on a bed 48 in a ward. The condition of the patient P is so bad that he or she cannot be brought to an X-ray room in which a stationary X-ray imaging apparatus is installed. Therefore, an operator (not shown) brings an electronic cassette 49 and an portable X-ray generating apparatus 34 to the patient's ward so as to perform imaging. The electronic cassette 49 can be detachably connected with a cable 5, through which data is transmitted and electric power is supplied, via a connector 50. The cable 5 is connected to a system control portion 27 and a power source portion 28 of the electronic cassette 49. The system control portion 27 controls the operations of the overall system such as control commands to the electronic cassette 49, receiving of digital image data and communication with the portable X-ray generating apparatus 34 etc. The power source portion 28 transforms an AC voltage of a commercial power source into a predetermined DC voltage for the electronic cassette 49 to supply it to the electronic cassette 49. The system control portion 27 and the power source portion 28 are accommodated in the same case having wheels (not shown) with a view to improving portability. The cable 5 is a composite cable including a signal line between the electronic cassette 49 and the control portion 27 and a power supply line between the electronic cassette 49 and the power source portion 28. Though two wires for a power system and a signal system respectively are included in the same cable, the wires are separated into a signal line and a power line at the cable end facing the power source portion 28 and the cable end facing the electronic cassette 49.
In one example of imaging, as a first step of the imaging process, the operator inserts the electronic cassette 49 that is not connected with the cable 5 between the patient P and the bed 48 at the position as shown in FIG. 7. The insertion is normally performed from a side of the patient as shown in FIG. 6. The reason why the electronic cassette 49 is inserted under the unconnected state is to eliminate the troublesome operation of determining the position of the electronic cassette while paying attention to the cable so that the cable will not fall into the imaging area. The electronic cassette 49 is positioned at the area in which an image of the patient to be obtained. After the electronic cassette 49 is positioned, the cable 5 is connected to the connector 50. Then, the operator performs, via an interface 30 of the system control portion 27 various setting such as setting of imaging conditions necessary for imaging (the X-ray tube voltage, the tube current and the X-ray irradiation time etc), imaging timing, image processing conditions, patient's ID, method of processing input images. The interface 30 includes a touch panel, a mouse, a keyboard or a foot switch etc. The system control portion 27 drives the portable X-ray generating apparatus 34 and the electronic cassette 49 based on the set imaging conditions. The portable X-ray generating apparatus 34 includes an X-ray tube 35 and an X-ray stop 37. The X-ray tube 35 is driven by a power source 36 for generating a high voltage controlled by the system control portion 27 to radiate an X-ray beam. The X-ray stop 37 shapes the X-ray beam in accordance with a change in the imaging area so that unnecessary X-ray irradiation is not performed. The X-ray beam is directed to the patient P lying on the bed 48. The electronic cassette 49 is irradiated with the X-ray beam that has been transmitted through the patient P. The electronic cassette 49 accommodates a scintillator for converting X-rays into visible light and a photo detector array as an X-ray receiving medium in which thin film transistors (TFT) are arranged similar to those disclosed in Japanese Patent Application Laid-Open No. 08-116043. An X-ray image of the patient that has been irradiated with the X-ray beam is converted into visible light by the scintillator in the interior of the electronic cassette 49 and the resultant visible light is subjected to photoelectric conversion in the photo detector array. After that, amplification processing and A/D conversion processing are performed, so that serialized digital image data is sent from the electronic cassette to the system control portion 27 via the signal line of the cable 5. The system control portion 27 performs switching of data to be displayed on a monitor 31, real time correction and spatial filtering of the digital image data, tone processing, DR compression etc. The processed image is displayed on the monitor 31. The processed digital data is stored in a memory apparatus 38 at the same time with the real time image processing. Preferably, the memory apparatus 38 is a data storage apparatus that meets large capacity, high speed and high reliability requirements. For example, hard disk arrays such as RAID are preferable. After the data is stored, the cable 5 is disconnected from the connector 50 and the electronic cassette 49 is drawn out from between the patient P and the bed 48. Thus the imaging process is terminated.
The system control portion 27 is provided with a LAN board (not shown), through which the system control portion 27 can be connected to a LAN. A file server in which image data is to be filed, an image printer for outputting an image on a film and an image processing terminal for facilitating complex image processing and diagnosis etc. are connected to the LAN. The system control portion 27 outputs digital image data in accordance with a predetermined protocol (for example, DICOM). After the imaging of the patient P is finished, the operator brings the system to a site at which a port for allowing connection to the LAN is available so as to perform an output operation. The port may be provided in the ward in which the patient P stays so that the output operation may be performed immediately after the completion of imaging.    (Reference: Japanese Patent Application Laid-Open No. 2002-82172)
However, the above-described structure of the electronic cassette suffers from the following problems.
FIG. 8 shows a case in which a connector provided on an electronic cassette 51 having the structure same as the above-described electronic cassette 49 is present between a patient P and a bed 48. This situation can occur in the case that the outer size of the electronic cassette 51 is smaller relative to the patient P. This is the case for example when the width of the body of the patient P is larger than the standard width or when the outer size of the electronic cassette is equivalent to the 12×10 inches size or 10×8 inches size in the case of the film cassette. When the operator places the electronic cassette in position, the cable 5 has not been connected yet. Then, it is necessary for the operator either to connect the cable while raising up the patient P or to once draw out the electronic cassette 51 and move the electronic cassette to a position which allows connection with the cable 5 so as to connect the cable. In any case, it is necessary to change the position relative to the patient P. In addition, there is a risk that the position of the electronic cassette can be displaced and the part to be imaged can deviate from the imaging area. In that case, imaging must be performed again. In addition, since the portable cassette is used not only in the above-described imaging manner but also in various positions for a patient who cannot move, it is necessary for the operator to perform imaging while always paying attention to the position of the connector of the electronic cassette. This is troublesome for the operator.